This invention relates to a method of marking or fingerprinting diamond material, in particular single crystal synthetic diamond material produced by chemical vapour deposition (hereinafter referred to as CVD), thereby providing a mark of origin or fingerprint in the diamond material, or a means by which its synthetic nature can more easily be determined. This method can also be exploited to generate single crystal diamond material of high colour.
Methods of depositing material such as diamond on a substrate by CVD are now well established and have been described extensively in patent and other literature. Where diamond is being deposited on a substrate, the method generally involves providing a gas mixture which, on dissociation, can provide hydrogen or a halogen (e.g. F, Cl) in atomic form and C or carbon-containing radicals and other reactive species, e.g. CHx, CFx wherein x can be 1 to 4. In addition, oxygen containing sources may be present, as may sources for nitrogen, and for boron. Nitrogen can be introduced in the synthesis plasma in many forms; typically these are N2, NH3, air and N2H4. In many processes inert gases such as helium, neon or argon are also present. Thus, a typical source gas mixture will contain hydrocarbons CxHy wherein x and y can each be 1 to 10 or halocarbons CxHyHalz wherein x and z can each be 1 to 10 and y can be 0 to 10 and optionally one or more of the following: COx, wherein x can be 0.5 to 2, O2, H2, N2, NH3, B2H6 and an inert gas. Each gas may be present in its natural isotopic ratio, or the relative isotopic ratios may be artificially controlled; for example hydrogen may be present as deuterium or tritium, and carbon may be present as 12C or 13C. Dissociation of the source gas mixture is brought about by an energy source such as microwaves, RF (radio frequency) energy, a flame, a hot filament or jet based technique and the reactive gas species so produced are allowed to deposit onto a substrate and form diamond.
CVD diamond may be produced on a variety of substrates. Depending on the nature of the substrate and details of the process chemistry, polycrystalline or single crystal CVD diamond may be produced.
The development in the level of sophistication of methods of producing CVD single crystal diamond has meant that this material is becoming increasingly more suitable for use in industrial applications or in ornamental applications such as synthetic gemstones for jewelry. However, in many applications there is a need to provide a method of determining the source of synthetic diamond used in these applications in order to verify its origins or synthetic nature.